Locally advanced or locally invasive solid tumors are primary cancers that have extensively invaded or infiltrated into the otherwise healthy tissues surrounding the site where the tumor originated. Locally advanced tumors may arise in tissues throughout the body, but unlike early stage tumors may not be amenable to complete surgical excision or complete ablation using radiation treatments. Due to the invasion of the surrounding tissues by tumor processes, any surgical procedure that would serve to remove all the cancerous cells would also be likely to maim or destroy the organ in which the cancer originated. Similarly, radiation treatments intended to eradicate the cancerous cells left behind following surgery frequently lead to severe and irreparable damage to the tissues in and around the intended treatment field. Often, surgery is combined with radiotherapy, chemotherapy or a combination of adjuvant therapies designed to eliminate the malignant cells that could not be removed by the surgery. However, when a tumor has infiltrated into otherwise healthy tissues surrounding the site where the tumor originated, even combination treatments including surgery plus therapy, or surgery plus therapy plus chemotherapy may not be capable of eradicating the tumor cells without causing severe damage to the tissues in the treatment field.
In cases involving locally advanced tumors, surgery may be used for gross excision, a procedure referred to as “debulking,” but the surgeon at present does not have the tools to eliminate individual tumor cells, microscopic tumor processes, or tumor-associated vasculature from the normal tissue surrounding the tumor excision site. It is often critical to minimize the volume of surrounding tissue that is excised in such operations. For example, in the case of tumors of the central nervous system, normal brain functions may be severely compromised as a result of tissue loss. Thus, in such cases surgery is often accompanied by radiation therapy and/or chemotherapy in an attempt to kill cancerous cells remaining in the surrounding brain tissue. The chemotherapy may be delivered to the residual tumor cells by a localized or systemic route of administration. By limiting the extent of surgical excision, and relying upon the adjunctive treatments to eliminate the residual cancer cells, the function of an organ may be preserved.
Conventional radiation therapy, using ionizing radiation beams (X-ray, gamma ray, or high energy beta particles), while well-established as an anti-cancer treatment modality, is not curative in the majority of patients whose cancer is locally advanced. Another form of radiation treatment is brachytherapy, the implantation of sealed radioactive sources emitting gamma rays or high energy beta particles within the tissue adjacent to the tumor site, for example in treatment of brain or prostate cancer. For example, see U.S. Pat. Nos. 6,248,057, 6,743,211, and 6,905,455.
Even with the combination of systemic agents and x-rays, nearly one third of patients with locally advanced solid tumors relapse locally without metastatic dissemination (Vijaykumar, S. and Hellman, S., “Advances in Radiation Oncology,” Lancet, 349[S11]: 1-3 (1997)). Ionizing radiation, whether from a beam or from an isotopic implant emitting high energy radiation, lacks the specificity needed to eliminate the tumor cells while sparing the normal cells within the treatment field. Thus, collateral damage to normal tissues cannot be avoided. Conventional radiation therapy has several additional limitations. X-rays are administered by an intermittent schedule, usually daily for 5 days per week, thereby providing an opportunity for the cancer cells to repair their DNA and to repopulate the tumor between treatments. Ionizing radiation requires sufficient oxygen in the tissues to eliminate tumor cells, but most solid tumors are relatively hypoxic, and therefore inherently resistant to radiation. In addition, the total lifetime dose of radiation is limited by the risk of severe late toxicities. Therefore, with few exceptions only a single treatment course, usually lasting no more than 6-7weeks, can be administered to a tumor. Finally, ionizing radiation is itself oncogenic, especially when used in combination with chemotherapy agents.
Most types of chemotherapy also suffer from a lack of tumor specificity and also cause collateral damage to normal tissues, since chemotherapeutic agents are distributed throughout the body and exert their effects on normal cells as well as malignant cells. Many systemic chemotherapy agents act on cells undergoing DNA synthesis and cell division, and thus may impact many cell populations throughout the body in addition to the target cancer cells.
A recent development that is critical for understanding the underlying biology of locally advanced solid tumors is the discovery of cancer stem cells, a minority subpopulation of the cells that comprise a tumor. For example, see Jordan, C. T. et al. Cancer Stem Cells. N. Eng J. Med. 355:1253-61 (2006) and Al-Hajj M et al. Therapeutic implications of cancer stem cells. Current Opinion in Genetics and Development. 14:43-47 (2004). In most tumors examined, the cancer stem cells comprise no more than 1% of the total tumor cell population, and yet these cells are responsible for maintaining the growth of the entire tumor by virtue of their capacity for self renewal and extended proliferation. When transplanted into immunocompromised rodents, only the cancer stem cells can form progressive tumors. In fact, cancer stem cells can recapitulate the distinctive microscopic architectural patterns characteristic of the original human tumor from which the cells were isolated.
Cancer stem cells are believed to proliferate rather slowly, and they represent only a small proportion of the cycling/dividing cells within a tumor (as observed at a given time). Cancer stem cells give rise to a more rapidly proliferating subpopulation of cancer cells, referred to as “transit-amplifying” or “progenitor” cancer cells, which comprise the vast majority of cycling/dividing cells observed in the tumor. The transit-amplifying cancer cells and cancer stem cells differ in multiple ways. Unlike the cancer stem cells, transit-amplifying cancer cells lack the capacity for self-renewal and undergo only a limited number of cell divisions before completely losing their proliferative capability. In contrast to cancer stem cells, transit-amplifying cancer cells cannot efficiently form progressive tumors when transplanted into immuno-compromised rodents.
Transit-amplifying cancer cells give rise to yet another subpopulation of cancer cells that cannot divide. These post-mitotic cancer cells comprise the majority of cells in many solid tumors. Thus, solid tumors are comprised of at least three distinct subpopulations of malignant cells, each endowed with a different capacity for cell division and continuing growth. Indeed, the vast majority of cells in most solid tumors cannot support progressive tumor growth or lead to tumor recurrence after an initial remission or response to treatment.
The tumor-shrinking and/or tumor-inhibiting activities of ionizing radiation and currently used anticancer drugs are believed to involve direct effects on the transit-amplifying cancer cells, and in many cases the blood vessels that supply tumors (For example, see Jordan, C. T. et al. Cancer Stem Cells. N. Eng J. Med. 355:1253-61 [2006]; and Fidler I. J. et al. “Angiogenesis” pp 129-136 in Cancer Principles and Practice of Oncology 7th edition. De Vita V T, Hellmann S and Rosenberg S A. Lippincott Williams & Wilkins © 2005). Applying the principles of stem cell biology to cancer. Nature Reviews Cancer 3:895-902 (2003); and Polyak K and Hahn W C. Roots and Stems: stem cells in cancer. Nature Medicine. 11:296-300 (2006). Neither of these two major treatment modalities is capable of eradicating locally advanced solid tumors without causing severe damage to the tissues in which the cancer originated, or preventing the recurrence of locally advanced solid tumors without causing severe damage to the tissues in which the cancer originated; and neither of these major treatment modalities is capable of producing long term remissions of most types of locally advanced solid tumors, even when used in combination. Ionizing radiation and currently used drugs usually provide only a short term effect on tumor growth.
Cancer stem cells have been referred to as the “root” of the tumor, and accordingly, the elimination of transit-amplifying and postmitotic cancer cell subpopulations has been likened to “weed whacking”, because it is invariably associated with re-growth of the tumor. The elimination of cancer stem cells is believed to be a prerequisite for curing advanced solid tumors, such as by identifying targeted agents that can selectively kill the cancer stem cells while sparing normal stem cells. For example see Pardal et al. Applying the principles of stem cell biology to cancer. Nature Reviews Cancer 3:895-902 (2003); Polyak K and Hahn W C. Roots and Stems: stem cells in cancer. Nature Medicine. 11:296-300 (2006); and Guzman M and Jordan C T. Considerations for targeting malignant stem cells in leukemia. Cancer Control. 11:97-104 (2004).
Cancer stem cells have been isolated and characterized in patients with many types of malignancies, including a particularly aggressive type of primary brain tumor referred to as “glioblastoma multiforme” or “GBM”. For example see Singh, S. K. et. al. Identification of human brain tumour-initiating cells. Nature 432:396-399 (2004); Galli R., et. al. Isolation and characterization of tumorigenic, stem-like neural precursors from human glioblastoma. Cancer Res. 64:7011-21 (2004). Sanai, N., Alvarez-Buylla, A. and Berger, M. S. 2005. Neural Stem Cells and the Origin of Gliomas N. Engl J. Med. 353:811-22. Because tumor stem cells are responsible for the maintenance of GBM tumors, this subpopulation of cells must be eliminated to prevent tumor recurrence following treatment, and to achieve long term survival in patients with these tumors.
Killing brain tumor stem cells presents a formidable challenge. There are four major obstacles standing in the way. First, recent studies using gene expression profiling indicate that solid tumors, including GBM, are much more genetically and metabolically heterogeneous than previously anticipated. For example, see Quackenbush, J. Microarray Analysis and Tumor Classification. N Eng J Med. 354:2463-72 (2006); Mischel, P. S. Cloughesy, T. F. and Nelson, S. F., “DNA-Microarray Analysis of Brain Cancer: Molecular Classification for Therapy,” Nature Cancer Reviews, 5:782-792 (2004). Solid tumors, as well as the cancer stem cells that drive their growth, appear to be genetically and metabolically heterogeneous despite a common organ or tissue of origin, and despite very similar appearances under the microscope. This is especially true of malignant gliomas, which arise in the central nervous system. For example, see Phillips et al. Molecular subclasses of high-grade glioma predict prognosis, delineate a pattern of disease progression, and resemble stages in neurogenesis. Cancer Cell 9:157-173 (2006). In view of the genetic/metabolic heterogeneity of solid tumors, biochemical targeting (i.e. the search for agents that specifically target the stem cells in each type of tumor) is a daunting challenge.
Second, brain tumor stem cells and other types of cancer stem cells are inherently resistant to chemotherapeutic agents, in part due to elevated expression of drug efflux transport proteins. For example, see Hirschmann-Jax C et al. A distinct “side population” of cells with high drug efflux capacity in human tumor cells. Proc. Natl. Acad. Sci. USA. 101; 14228-14233 (2004); Kondo T. et al Persistence of a small subpopulation of cancer stem-like cells in the C-6 glioma cell line. Proc. Nat. Acad. Sci. USA. 101: 781-786 (2004); and Jordan, C. T. et al. Cancer Stem Cells. N. Engl J. Med. 355:1253-61 (2006).
Third, brain tumor stem cells are resistant to ionizing radiation due to the preferential induction of DNA damage-response genes that repair DNA damage caused by radiation. For example, see Bao, S. et al. Glioma stem cells promote radioresistance by preferential activation of the DNA damage response. 2006. Nature 444:756-710.
Finally, brain tumor stem cells are believed to proliferate more slowly than other cell populations within the tumor thereby making them less susceptible to the toxic effects of cell cycle active agents and ionizing radiation. For example, see Jordan, C. T. et al. Cancer Stem Cell. N. Engl J. Med. 355:1253-61 (2006). Pardal et al. Applying the principles of stem cell biology to cancer. Nature Reviews Cancer 3:895-902 (2003); Polyak K and Hahn W C. Roots and Stems: stem cells in cancer; Nature Medicine. 11:296-300 (2006). Cancer stem cells are also believed to proliferate/cycle at a slower rate than their immediate progeny, the transit-amplifying cancer cells (see Vescovi A L et al. Brain Tumor Stem Cells. Nature Reviews—Cancer, 6:425-436 (2006); Sanai N et al. Neural Stem Cells and the Origin of Gliomas. N Eng J Med 353 811 (2005); and Singh et al. Cancer stem cells in nervous system tumors. Oncogene, 23, 7267-7273 (2004). These challenges notwithstanding, tumor stem cells represent a defined cellular target for new anticancer treatments.
Certain drugs can block the progression of tumor cells out of S-phase, thus effectively increasing the fraction of susceptible cells within the target cell population. For example, see Chu E. “Principles of Medical Oncology”, pp 295-306 in Cancer Principles and Practice of Oncology 7th edition. De Vita V T, Hellmann S and Rosenberg S A eds. Lippincott Williams & Wilkins © 2005. Combining a cell-cycle inhibitory agent with an S-phase active cytotoxic agent is a well established treatment principle. In fact, this approach has been used successfully using a cell cycle inhibitor, 5-fluorouridine 2′ deoxyribonucleoside, to increase the uptake and incorporation of 125IUDR into DNA. For example, see: Holmes, J. M. The toxicity of fluorodeoxyuridine when used to increase the uptake of 125I-iododeoxyuridine into tissue culture cells in vitro. J Comp Pathol. 93:531-539 (1983); F. Buchegger et al Highly efficient DNA incorporation of intratumourally injected [125I]iododeoxyuridine under thymidine synthesis blocking in human glioblastoma xenografts. Int J Cancer 110:145-149 (2004); and Perillo-Adamer, F. Short fluorodeoxyuridine exposure of different human glioblastoma lines induces high-level accumulation of S-phase cells that avidly incorporate 125I-iododeoxyuridine. Eur J Nucl Med Mol Imaging 33: 613-620 (2006). This approach is unlikely to be amenable to cancer stem cells, which may not proliferate with sufficient rapidity to be susceptible to cell cycle blockade.
Another treatment strategy is to combine a mitogenic growth factor with an S-phase active cytotoxic agent; however, in practice, this approach has not been particularly useful. One problem has been that numerous mitogenic growth factors have the potential to stimulate the growth of tumors, which counteracts the desired effect of the treatment (i.e. tumor shrinkage). Another problem is that the addition of a mitogenic growth factor to an S-phase active cytotoxic agent may increase the toxicity of the cytotoxic agent towards cycling cells in normal tissues, including normal stem cells and normal transit-amplifying cells in the brain, bone marrow, oral mucosa, gut, skin, hair and/or germ cells. For example, while FGF-2, EGF and PDGF may cause tumor stem cells to enter S-phase of the cell cycle (i.e. initiate DNA synthesis), these mitogenic growth factors may also stimulate normal neural progenitor cells to enter S-phase in various regions of the CNS (see Palmer T D et al. Fibroblast growth factor-2 activates a latent neurogenic program in neural stem cells from diverse regions of the adult CNS. J. Neurosci. 19: 8487-8497 [1999]; Jackson, E L et al. PDGF-alpha positive B cells are neural stem cells in the adult SVZ that form glioma like growths in response to increased PDGF signaling. Neuron 51:187-199 [2006]; and Gritti, A et al. Epidermal and Fibroblast Growth Factors Behave as Mitogenic Regulators for a Single Multipotent Stem Cell-Like Population from the Subventricular Region of the Adult Mouse Forebrain J. Neurosci, 19:3287-3297 [1999]).
Macular degeneration is a medical condition predominantly found in elderly adults in which the center of the inner lining of the eye, known as the macula area of the retina, suffers thinning, atrophy, and in some cases, bleeding. This can result in loss of central vision, which entails inability to see fine details, to read, or to recognize faces. It is the leading cause of central vision loss (blindness) in the United States today for those over the age of fifty years. Although some macular dystrophies that affect younger individuals are sometimes referred to as macular degeneration, the term generally refers to adult or age-related macular degeneration (AMD or ARMD).
Advanced AMD, which is responsible for profound vision loss, has two forms: dry and wet. Central geographic atrophy, the dry form of advanced AMD, results from atrophy to the retinal pigment epithelial layer below the retina, which causes vision loss through loss of photoreceptors (rods and cones) in the central part of the eye. Neovascular or exudative AMD, the wet form of advanced AMD, causes vision loss due to abnormal blood vessel growth in the choriocapillaries, through Bruch's membrane, ultimately leading to blood and protein leakage below the macula. Bleeding, leaking, and scarring from these blood vessels eventually cause irreversible damage to the photoreceptors and rapid vision loss if left untreated.
Until recently, no effective treatments were known for wet macular degeneration. However, new drugs, called anti-angiogenics or anti-VEGF (anti-Vascular Endothelial Growth Factor) agents, when injected directly into the vitreous humor of the eye using a small needle, can inhibit growth of abnormal blood vessels and improvement of vision. The injections usually have to be repeated on a monthly or bi-monthly basis. Examples of these agents include anti-VEGF antibodies (Lucentis and Avastin) and anti-VEGF apatamers (e.g. Macugen).
A unique cell killing mechanism that has garnered considerable interest is the release of Auger electrons. These electrons are emitted by radionuclides that decay by electron capture and internal conversion. Examples of Auger emitting radionuclides include 123Iodine, 124Iodine 125Iodine, 77Bromine, 80mBromine and 211Astatine. Auger electrons have energies even lower than the energy of the beta particle emitted by tritium. This effect is amplified, because some Auger emitters release multiple electrons with each nuclear transformation. The low energy of the Auger electrons results in extremely short particle path lengths within tissues, which is highly desirable, because it minimizes collateral damage.
One molecular entity incorporating 125Iodine is [125I]-iodouridine-deoxyriboside (125IUDR), a thymidine analog. 125IUDR is recognized by DNA polymerases as a normal thymidine metabolite, and thus is incorporated into the chromosomes at times of DNA synthesis. Once incorporated into the DNA, the Auger electrons, with their very short range (often less than 10 nm), have access to the chemical backbone of the DNA duplex. For example, see Martin R F and Haseltine W A. Range of radiochemical damage to DNA with decay of Iodine-125. Science 213:896-898 (1981); and Kassis A I et al. Kinetics of uptake, retention, and radiotoxicity of 125IUDR in mammalian cells: implications of localized energy deposition by Auger processes. Radiation Research 109:78-89 (1987). When the 125Iodine atom disintegrates, Auger electrons have the potential to cause severe damage to chromosomes with minimal effect on cells in the immediate vicinity of the target cell. For example, see U.S. Pat. No. 5,077,034. 125IUDR also releases high energy gamma photons during internal conversion; therefore, this agent has the potential to damage DNA by two very different types of radiation.
Despite the recognition that 125IUDR has a unique cell killing capability, and despite many years of research aimed at exploiting this mechanism of action, including the concept of directly introducing 125IUDR into tumors (for example, see Kassis et. al. Treatment of tumors with 5-radioiodo-2′-deoxyuridine. U.S. Pat. No. 5,077,034), these agents have not been successfully applied to the treatment of cancer. The delivery of 125IUDR and related agents to solid tumors, using systemic or local administration, has proven to be extremely challenging. New approaches are needed to deliver 125IUDR (and related compounds) to solid tumors with the intent to eliminate the tumor-maintaining stem cells while at the same time sparing normal tissues that have been invaded by the cancer cells. This includes novel devices to deliver such agents directly into the tumors, and into the normal tissues that have been invaded by tumor cells, as described in Matsuura and Warren (Catheter and array for anticancer therapy (U.S. patent application Ser. No. 60/895,916). In addition, 125IUDR has not been used to treat non-neoplastic disorders characterized by pathological, unwanted cell proliferation.
In various embodiments the bioactive agent can include Auger-electron emitting radionucleoside or an analog or a prodrug thereof, such as a halogenated nucleoside analog, for example 5-[123I]-iodouridine 2′-deoxyribonucleoside, 5-[124I]-iodouridine 2′-deoxyribonucleoside, 5-[125I]-iodouridine 2′-deoxyribonucleoside, 5-[77Br]-bromouridine 2′deoxyribonucleoside, 5-[80mBr]-bromouridine 2′-deoxyribonucleoside, 8-[123I]-iodoadenine 2′-deoxyribonucleoside, 8-[124I]-iodoadenine 2′-deoxyribonucleoside, 8-[125I]-iodoadenine-2′-deoxyribonucleoside, 5-[77Br]-bromoadenine 2′-deoxyribonucleoside, 5-[80mBr]-bromoadenine 2′-deoxyribonucleoside, 5-[211At]-astatouridine 2′-deoxyribonucleoside, or 8-[211At]-astatoadenine 2′-deoxyribonucleoside. In various embodiments the bioactive agent can include an Auger-electron emitting nucleoside prodrug, such as a 3′- or 5′-phosphate or carboxylate ester of a deoxyribosyl or ribosyl moiety of the radionucleoside. In various embodiments, the bioactive agent can include a second medicament, such as an anticancer drug, an antiinflammatory drug, or an antibiotic.
Coadministration of mitogens and S-phase active agents, e.g. 125IUDR and other radionucleosides, as a method to eliminate neoplastic and non-neoplastic pathological cell proliferation, has not been feasible without exposing normal stem cells, e.g. resident populations in the brain, bone marrow, oral mucosa, gut, skin, hair, and germ cells, to such potentially lethal combinations.